As soon as 2014, the Burj Khalifa[1] may no longer be the tallest building in the world. Sky City[2], a planned 220-story prefab tower in Changsha, China, will soon claim that title. According to Lloyd Alter at Treehugger[3], Broad Sustainable Building[4], the company behind the tower, will begin construction on the prefab behemoth this June. The energy-efficient skyscraper will literally house an entire city using just 10 percent of the site area, and it could serve as a model for sustainable urban development of the future.

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Sky City[7] will be prefabricated off site in three months, and it will then be assembled in just seven months. Reaching up 838 meters (2,749 feet), the 220-floor tower will feature residential, office space, organic farms, recreation spaces, schools, a hospital retail and much more. The tower will house 4,450 families in apartments ranging from 645 square feet to 5,000 square feet with 92 elevators at your disposal to reach them. As its name suggest, Sky City will be a vertical city that will accommodate 100,000 people and offer everything that is needed — water, electricity, sewage (unlike the Burj Khalifa[8]), open space, schools, health care and more.

Using just a portion of its site, Sky City will be home to the most extreme urban density[9] we’ve ever seen. But the difference between Sky City and say, Hong Kong, is that the tower will be surrounded by parks, meaning that every resident will have access to open space. The prefabricated tower will include many energy efficient strategies like 8-inch thick insulated walls, triple glazing, exterior shading that cuts down on cooling by 30 percent, and a co-generation plant that will use waste heat from power generation for heating and cooling. Transportation will be provided by low-energy elevators and for those who want to walk (or get exercise) there is a six-mile-long ramp running from the first to the 170th floor.

According to Treehugger[3], construction is set to begin this June and is expected to be complete within seven months (210 days). The rapid pace of construction and the overall design for such a massive skyscraper could be a cause of concern, but if Broad Sustainable Building[4] pulls it off, it may show the world how sustainable density can be achieved on a massive scale. The company assures that the building will be able to withstand a Magnitude 9 earthquake and will have a three-hour fire resistance rating.

Lloyd Alter[3] at Treehugger sums it up well: “This is going to be a controversial vision of sustainability; putting 30,000 people in a single building is a hard sell. It is not the bucolic version of green living that most people think of. It certainly is a lot higher than what I have called the Goldilocks Density[10]. But it is the logical extension of the Edward Glaeser[11] / David Owen[12] thesis that the way to go green is to go up, reducing the amount of land used per person and the distances people travel.” A resident of Sky City will use 1/100th the average land per person as a regular global resident and will use only 2 tons of CO2 compared to 5.5 per capita.